1. Field of the Invention
The present invention relates to a relief valve for a positive displacement pump and, more particularly, but not by way of limitation, to a removable valve seat for the relief valve needle wherein the removable valve seat prevents damage to the pump housing.
2. Description of the Related Art
An important use for a positive displacement pump includes its connection to the carbonator of a carbonated beverage dispensing system. The positive displacement pump supplies water to the carbonator where it is entrained with CO.sub.2 gas to form the carbonated water necessary to furnish a carbonated beverage from the carbonated beverage dispensing system. Specifically, the inlet into the positive displacement pump connects to a water supply, while the outlet from the pump connects to the inlet into the carbonator. The carbonator further connects to a CO.sub.2 source which delivers CO.sub.2 gas into the carbonator with sufficient pressure (approximately 100 psi) to carbonate the water delivered from the positive displacement pump.
FIG. 1 depicts an existing positive displacement pump suitable for use in carbonated beverage dispensing systems. Such a positive displacement pump is disclosed in U.S. Pat. No. 2,925,786, issued Feb. 23, 1960 to Hill. Positive displacement pump 10 includes housing 11 which typically is fabricated from brass. Housing 11 defines pump chamber 12 which contains a vaned pump rotor (not shown). Inlet 13 connects to a water supply and outlet 14 connects to the carbonator (not shown). Thus, when the carbonator requires water, a pump motor (not shown) activates to turn the rotor within pump chamber 12. As a result, the rotor draws water from the water supply through passageway 23 and forces it through passageway 24, out outlet 14, and into the carbonator. Passageway 23 typically contains a strainer (not shown) which is removed and replaced through opening 22. However, during operation of positive displacement pump 10, opening 22 is sealed using a strainer cap.
Positive displacement pump 10 further includes relief valve 15 which permits a pump user to set the pressure at which positive displacement pump pumps water into the carbonator (approximately 170 psi). Relief valve 15 includes needle 16 which resides within passageway 17 of housing 11. Spring 18 resides between the head of needle 16 and set screw 19 to apply pressure against needle 16 and force needle 16 within passageway 17. Set screw 19 threadably connects to housing 11 and provides adjustments in the tension spring 18 exerts against needle 16. Those adjustments provide different pumping pressures for positive displacement pump 10 because they change the point at which relief valve 15 opens to bypass the water driven from pump chamber 12. That is, when the pressure of the water pumped from pump chamber 12 exceeds the user set pressure level, the water enters passageway 17 and forces needle 16 away from edges 20 and 21 at the outlet from passageway 17. Consequently, the pumped water flows through passageway 17 thereby stopping the delivery of water into the carbonator to prevent damage to either the carbonator or the pump motor.
Without relief valve 15, positive displacement pump 10 would damage the carbonator if the pressure of the water delivered into the carbonator exceeded the user set level. That is, if relief valve 15 did not bypass the pumped water when it exceeded the user set level, positive displacement pump 10 would pump water into the carbonator until the seals on the carbonator burst. Alternatively, if the pressure in the carbonator overcomes the ability of the pump motor to drive water into the carbonator, the rotor would seize, resulting in the pump motor burning out.
Accordingly, relief valve 15 plays an integral part in the proper functioning of positive displacement pump 10. Unfortunately, because housing 11 comprises brass, the flow of water past edges 20 and 21 of passageway 17 causes erosion of those edges. That is, the velocity of the water combined with the minerals in the water wear edges 20 and 21 away. When the flowing water sufficiently rounds edges 20 and 21, needle 16 no longer seats sufficiently over the outlet from passageway 17 to prevent water flow through passageway 17 at pressures below the user set pump pressure level. Consequently, positive displacement pump 10 fails to supply water to the carbonator at a sufficient volume and pressure to permit proper carbonation. Without proper carbonation, the carbonated beverage dispensed from the carbonated beverage dispensing system tastes poorly.
Presently, positive displacement pumps such as positive displacement pump 10 operate effectively for less than a year. When positive displacement pump 10 ceases to operate at an acceptable level, pump housing 11 is typically remachined. Unfortunately, remachining is expensive and often impractical because the necessary equipment might not be available. Furthermore, edges 20 and 21 are often eroded to the point where remachining of pump housing 11 is impossible. In such instances, positive displacement pump 10 is replaced and pump housing 11 is discarded. However, the discarding of pump housing 11 is not practical because it is extremely expensive in comparison to the remaining parts of positive displacement pump 10. Thus, the disposal of pump housing 11 is an extremely wasteful consequence of the erosion occurring at edges 20 and 21 of passageway 17.
Accordingly, a positive displacement pump and relief valve design is required which prevents the unnecessary machining or disposing of the entire pump housing when the edges at the outlet from the relief valve passageway erode.